Angular Acceleration.

A circular saw blade completes 1200 revolutions in 40s while coasting to a stop after being turned off. Assuming constant deceleration, what are (a) the angular deceleration and (b) the initial angular speed?

Answer in RPM/S
Method I used: Change in theta is 1200
Time: 40s
final Vel.:0
Initial Vel.:?
Alpha:? Eqn Used: (change in theta)=(1/2)(Initial vel.+final vel.)*time
looking for inital speed:
1200=(1/2)(initial vel+0)40seconds
Take the vel. found and place into eqn:
looking for alpha:
final vel. =Initial vel.+alpha*time